1. Technical Field
The present invention relates to a resonator, and an oscillator, an electronic apparatus, and a mobile object each equipped with the resonator.
2. Related Art
A quartz crystal resonator, in which a quartz crystal resonator element vibrating in a thickness-shear vibration mode as a vibration mode of the principal vibration is used, is suitable for miniaturization and higher frequency, and is superior in a frequency-temperature characteristic, and is therefore used in a variety of fields such as an oscillator and electronic equipment. In particular, in recent years, there have been used quartz crystal resonators each functioning as a reference clock in order to control an electronic control unit (ECU) such as an antilock brake system (ABS), a tire pressure monitoring system (TPMS), an engine control system, or a vehicle attitude control system installed in a vehicle.
Such quartz crystal resonators are each formed by mounting a quartz crystal resonator element provided with excitation electrodes in a cavity formed of, for example, a ceramic package (base), and then bonding a lid to the base to thereby closely seal the inside of the cavity. Further, in JP-A-2012-178633 (Document 1) and International Publication No. 2013/168339 (Document 2), there has been disclosed a quartz crystal resonator (a piezoelectric device) having a so-called clamped-clamped type four-point support structure, in which the four corners of the quartz crystal resonator element are supported in order to improve the vibration resistance and the impact resistance, for in-car use.
However, in the piezoelectric device (quartz crystal resonator) described in Document 1 or Document 2, in the case of the shape obtained by applying convex or bevel machining to the piezoelectric resonator element (resonator element), the resonator element gradually decreases in thickness from the central region toward end regions so that the outer edge of the cross-sectional surface of the resonator element curves. Therefore, the gap from an attachment surface of the base (container) to the resonator element becomes high, and when fixing the corner portion of the resonator element to the base, it is required to increase an amount of bonding material in order to ensure the bonding strength. Therefore, the leakage of the vibration energy toward the base increases due to the decrease in distance between the vibrating region and the bonding material. Further, the volume of the bonding material increases, and the mounting stress increases accordingly. Therefore, there has been a problem that the equivalent series resistance value of the piezoelectric device is deteriorated.